✨ implement zoom-to-mouse in CameraSystem

Replaces plain cam.setZoom() with zoom-to-mouse: after each zoom step
the scroll is corrected by (mouseOffset from center) * (1/zBefore - 1/zAfter),
keeping the world point under the cursor fixed. Also fixes getCenterWorld()
which previously divided by zoom incorrectly. Added JSDoc to all methods.

src/systems/CameraSystem.ts

@@ -27,11 +27,19 @@ export class CameraSystem {
   private lastPanX = 0
   private lastPanY = 0
 
+  /**
+   * @param scene   - The Phaser scene this system belongs to
+   * @param adapter - Network adapter used to persist camera position
+   */
   constructor(scene: Phaser.Scene, adapter: LocalAdapter) {
     this.scene = scene
     this.adapter = adapter
   }
 
+  /**
+   * Initializes the camera: restores saved position, registers keyboard keys,
+   * sets up scroll-wheel zoom-to-mouse, and middle-click pan.
+   */
   create(): void {
     const state = stateManager.getState()
     const cam = this.scene.cameras.main
@@ -52,10 +60,22 @@ export class CameraSystem {
       d:     kb.addKey(Phaser.Input.Keyboard.KeyCodes.D),
     }
 
-    // Scroll wheel zoom
+    // Scroll wheel: zoom-to-mouse.
-    this.scene.input.on('wheel', (_ptr: Phaser.Input.Pointer, _objs: unknown, _dx: number, dy: number) => {
+    // Phaser zooms from the screen center, so the world point under the mouse
-      const newZoom = Phaser.Math.Clamp(cam.zoom - Math.sign(dy) * ZOOM_STEP, MIN_ZOOM, MAX_ZOOM)
+    // is corrected by shifting scroll by the mouse offset from center.
+    this.scene.input.on('wheel', (ptr: Phaser.Input.Pointer, _objs: unknown, _dx: number, dy: number) => {
+      const zoomBefore = cam.zoom
+      const newZoom = Phaser.Math.Clamp(zoomBefore - Math.sign(dy) * ZOOM_STEP, MIN_ZOOM, MAX_ZOOM)
       cam.setZoom(newZoom)
+
+      const factor = 1 / zoomBefore - 1 / newZoom
+      cam.scrollX += (ptr.x - cam.width  / 2) * factor
+      cam.scrollY += (ptr.y - cam.height / 2) * factor
+
+      const worldW = WORLD_TILES * 32
+      const worldH = WORLD_TILES * 32
+      cam.scrollX = Phaser.Math.Clamp(cam.scrollX, 0, worldW - cam.width  / newZoom)
+      cam.scrollY = Phaser.Math.Clamp(cam.scrollY, 0, worldH - cam.height / newZoom)
     })
 
     // Middle-click pan: start on button down
@@ -86,6 +106,10 @@ export class CameraSystem {
     })
   }
 
+  /**
+   * Moves the camera via keyboard input and periodically saves the position.
+   * @param delta - Frame delta in milliseconds
+   */
   update(delta: number): void {
     const cam = this.scene.cameras.main
     const speed = CAMERA_SPEED * (delta / 1000) / cam.zoom
@@ -103,7 +127,7 @@ export class CameraSystem {
 
     if (dx !== 0 && dy !== 0) { dx *= 0.707; dy *= 0.707 }
 
-    const worldW = WORLD_TILES * 32  // TILE_SIZE hardcoded since WORLD_PX may not exist
+    const worldW = WORLD_TILES * 32
     const worldH = WORLD_TILES * 32
     cam.scrollX = Phaser.Math.Clamp(cam.scrollX + dx, 0, worldW - cam.width / cam.zoom)
     cam.scrollY = Phaser.Math.Clamp(cam.scrollY + dy, 0, worldH - cam.height / cam.zoom)
@@ -120,14 +144,24 @@ export class CameraSystem {
     }
   }
 
+  /**
+   * Returns the world coordinates of the visual camera center.
+   * Phaser zooms from the screen center, so the center world point
+   * is scrollX + screenWidth/2 (independent of zoom level).
+   * @returns World position of the screen center
+   */
   getCenterWorld(): { x: number; y: number } {
     const cam = this.scene.cameras.main
     return {
-      x: cam.scrollX + cam.width / (2 * cam.zoom),
+      x: cam.scrollX + cam.width  / 2,
-      y: cam.scrollY + cam.height / (2 * cam.zoom),
+      y: cam.scrollY + cam.height / 2,
     }
   }
 
+  /**
+   * Returns the tile coordinates of the visual camera center.
+   * @returns Tile position (integer) of the screen center
+   */
   getCenterTile(): { tileX: number; tileY: number } {
     const { x, y } = this.getCenterWorld()
     return { tileX: Math.floor(x / 32), tileY: Math.floor(y / 32) }